No one looks their age in Wildlife, the new 1960s-set coming-of-age drama that marks Paul Dano’s directorial debut. Even taking into account the earlier ages at which past generations started families, it takes a few scenes to believe the boyish Jake Gyllenhaal and the cherub-cheeked Carey Mulligan as the parents of a teenager. But Wildlife soon turns that disjunction into a strength, as 14-year-old Joe (a sad-eyed Ed Oxenbould) is forced to adapt to his parents’ abandonment of their responsibilities—first by his ne’er-do-well father Jerry, then in subtler but far more hurtful ways by his fed-up mother Jeanette. Joe’s home life isn’t so much turned upside down as it is slowly wrenched apart, as each member of the Brinson family begins to assert their competing visions for the future.

Adapted from Richard Ford’s novel of the same name, Wildlife is a confident and compassionate first film. But with its protagonist mostly relegated to waiting and observing, its main raison d’être is Mulligan’s masterful turn as a thirtysomething woman coldly testing her abilities to see what she’s capable of, while terrified that she won’t be able to provide a good life for her son. In the earliest scenes, Mulligan’s all spun sugar—so sweet and fluffy and undemanding you almost forget the effort that goes into such a performance (by both the actress and the character).

When the unemployed Jerry signs up to fight the dangerous wildfires devastating the mountains above their small town in Montana, a high-risk job low in pay and status, Jeanette treats his temporary desertion like the conclusion of a chapter of her life. (“We haven’t been intimate lately,” she half-explains to her son.) It’s intriguingly unclear whether Jeanette is more reckless or canny when she sets her sights on a wealthy, older, largely charmless divorcee (Bill Camp)—the kind of man that’s easy to seduce into bed but difficult to tempt into marriage. Her moods ever-shifting and her voice bouncing between octaves, Jeanette tries on different masks to see which one will get her what she wants, then loses patience when she isn’t winning her game fast enough.

Wildlife takes its title from the animals that Joe imagines fleeing the raging fires—he, too, is a refugee from the domestic idyll that he saw burn up before his eyes. The script, by Dano and his partner Zoe Kazan, would have benefited from a firmer sense of the social milieu in which Jeanette decides to break every rule that stands in her way. There’s something feminist about Jeanette’s one-sided ending of an unhappy marriage, of course, but the character is much more interesting for being an uncategorizable mystery, often to herself. She’s practical, except when she’s impetuous. Her aspirations are simultaneously lofty and grubby. When she gets drunk in the older divorcee’s home, openly flirting with the businessman in a barely-there dress in front of her confused and quietly seething son, Jeanette is hard to empathize with, and harder still to judge.

Playing the film’s most unintentionally destructive force, Mulligan is as fluctuant as a flame, as Jeanette attempts to sew together the young beauty queen she had to stop being when she impulsively got hitched and the world-weary cynic who teaches her son that feeling sorry for the unfortunate is fundamentally pointless. But the film’s center of gravity is so tilted toward her that there’s little of note in the scenes devoted to Jerry and Joe. (The reserved boy’s inertness is particularly frustrating, even if his helpless paralysis is altogether believable.) Gyllenhaal evinces some of that unpredictable propulsion, too, but the raw nerve Mulligan embodies is so transfixing that, while the film’s resolution is cogent and satisfying, it’s an inevitable letdown when it has to suture everything up.

Fortunately, Jeanette’s fieriness is matched by the pastel majesty of the mountains towering over the town, and later, the apocalyptic terror of the inferno that converts proud trees into “the standing dead.” (Wildlife was partly shot in Montana and for non-residents might well be more transporting geographically than chronologically.) Dano’s stiff, painterly compositions—some recalling Andrew Wyeth in their austerity and faces turned away from the viewer—eventually give way to more naturalistic scenes showcasing Mulligan’s transformations and the push-pull of attraction and repulsion Joe increasingly feels toward his mother. He can’t turn away, and neither can we.